Lucas targeted Star Wars at "young people" (his quote from 1977). He wanted to give them something fun and adventurous like the Flash Gordon TV series that he grew up with. In fact, he invented the world of Star Wars because he couldn't secure the rights to make a Flash Gordon movie. Anyways, the Flash Gordon TV series ran from 1954-55. Lucas was born in 44, so he was at least 10 or 11 and probably even as old as 14 or 15 if he watched it on re-runs. In other words, it's probable that he was targeting 10-15 year olds, or pre-teens to early teens. That's hardly "kiddie" age, and even saying that it's "for children" isn't fair, IMO, since we generally think of children as under 10.
I, personally, have no problem with admitting that Star Wars was targeted at pre-teens and early teens. That doesn't mean that it's only for them, though. Lucas was not dumb enough to make a multimillion-dollar movie that appealed only to 10-15 year olds. He wrote and directed it in such a way that it didn't feel like it was targeted at any age group, which helped many different age groups to embrace it. I'm not sure that I agree with correcting adults who claim that the movie was made for them because they're not entirely incorrect. It's not primarily made for them, no, but there's nothing in it that screams "kiddie content" or would turn off an adult. After all, Lucas was in his 30s when he developed it, and he presumably made a movie that he would like.